Despite their high level of performance in specific areas, such as weight, durability and through-life costs, composites are not widely accepted in primary structures. This is mostly due to a reduced understanding of the failure mechanisms and of their behaviour when damaged. This widespread lack of knowledge and know-how often leads to over sized structures, which are in contrast with the lightweight philosophy characterizing all the new design solutions.
Buckling still represents one of the most controversial issues of reinforced panel design. It is well known that composite stiffened panels can carry in plane loads higher than the buckling load without any failure. Unfortunately, the complexity and expensiveness of tests to simulate such behaviours associated with the destructiveness of the structure failure, makes the retrieving of failure mechanisms from the debris very complex.
For metallic airframes, stress release and redistribution are intrinsically provided by local plastic deformations and failure occurs by yielding of the skin or by local/global stiffener buckling. Local plasticization happens very seldom in composites, so this method of stress release is generally not available.